Add a keys argument to tapas

Add a keys argument to tapas that allows specifying devkeys to
use internal aosp_devkeys_* products that use the internal
devkeys, which will allow building unbundled apps that use platform
keys for testing.

Bug: 216553104
Test: tapas CarMediaApp devkeys
Change-Id: I2161be9e15f99713e11d22901d6eb7ad3c420093
diff --git a/tapasHelp.sh b/tapasHelp.sh
index 0f46130..7cb5f2c 100755
--- a/tapasHelp.sh
+++ b/tapasHelp.sh
@@ -6,7 +6,7 @@
 cd ../..
 TOP="${PWD}"
 
-message='usage: tapas [<App1> <App2> ...] [arm|x86|arm64|x86_64] [eng|userdebug|user]
+message='usage: tapas [<App1> <App2> ...] [arm|x86|arm64|x86_64] [eng|userdebug|user] [devkeys]
 
 tapas selects individual apps to be built by the Android build system. Unlike
 "lunch", "tapas" does not request the building of images for a device.